Open-label trial determining the efficacy of oral FK-506 in children with severe colitis unresponsive to steroid therapy after 1 week; to control the fulminant colitis, and as an alternative to intravenous cyclosporine or colectomy. Standard treatment has changed little over the past twenty years. The patient is placed on IV nutrition and given nothing by mouth, and corticosteroids are administered when concern of a precipitating enteric infection is eliminated, with broad spectrum antibiotics given if an infectious complication, such as toxic megacolon, is suspected. Several studies in adult patients suggest that patients who do not respond to such therapy over a 2-week period do not respond to continued standard therapy, and require surgery. The only proven recourse is colectomy and ileostomy. In a child, adjustment to colectomy and changes in image resulting from an ileostomy can be difficult. Potential benefits to the patient receiving FK-506 therapy include avoidance of colectomy, fewer intravenous lines and shorter hospitalization. Specific objectives include: 1) determining whether oral FK-506 is effective therapy for children with severe colitis above and beyond a prolonged course of corticosteroids; 2) determining the adverse effects of FK-506 when used in this setting; and 3) determining the impact of such therapy on systemic and mucosal immunity in these patients.